Polyimide has also been applied in many cases as a heat resistant adhesive used not only in the field of aerospace, but also in the field of electronics or the like requiring heat resistance from the facts that heat resistance, chemical resistance, mechanical strength, electrical characteristics and the like are excellent. Furthermore, a polyimide metal laminate plate has been used for a base material for a printed circuit board or the like, mainly as a circuit board material. In recent years, with miniaturization and high-density trend in electronic equipment, high-density trend and multilayer trend in printed circuit boards have also been attempted and a via hole for the interlayer wire connection has also been required to be not more than 50 μm. So, the via hole formation technique using a CO2 laser has been increased rather than the via hole formation technique by the conventional drilling processing. There has been a problem in the via hole formation process using a CO2 laser such that a polyimide type adhesive was not completely removed during CO2 laser processing and remained at the bottom of the via hole as a smear and it was hard to remove such a smear even in a desmear process. Thus, polyimide type adhesives in which a smear is easily removed in a desmear process by an alkali solution or the like and which have properties such as low-temperature adhesive property and high adhesion, in addition to heat resistance, have been in demand.
As a polyimide type adhesive having sufficient heat resistance and low-temperature adhesive property, there has been developed, for example, a resin comprising a polyamic acid (a precursor of a polyimide) and/or polyimide and a specific bismaleimide compound as disclosed in JP-A2004-209962 (Patent Document 1). The resin composition disclosed in the patent document surely had low-temperature adhesive property and excellent heat resistance. However, there has been a problem such that a smear was hardly removed in a desmear process mainly by a permanganate aqueous solution or the like.
On the other hand, as a polyimide resin using a diphenylsulfone tetracarboxylic dianhydride and a specific diamine compound, there has been known a polyimide resin as described in JP-A2001-6437 (Patent Document 2) or the like. In the patent document has been disclosed a polyimide resin useful as a printed circuit board which has realized a low dielectric property. However, a specific diamine compound was used for the resin composition described in the patent document 2 so that the problem in the desmear process as described above could not be solved.